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### Course: Organic chemistry>Unit 2

Lesson 1: Counting electrons

# Comparing formal charges to oxidation states

How formal charges and oxidation states are both ways of counting electrons.

## Want to join the conversation?

• Why are the definitions "hypothetical"? Are formal charges solely hypothetical or are they practical?
• The most useful definition of hypothetical for you would be : "supposed but not necessarily real or true."

In this instance, the hypothetical charge is the charge calculated by assuming either a) bonding electrons are shared equally or b) bonding electrons are assigned to the more electronegative atom

Therefore, these are hypothetical values because they are only true after we have made some assumption. They are not intrinsic to the atoms themselves.
• what is the use of formal charge or oxidation number??
• Understanding formal charge and oxidation states really helps with understanding mechanisms of reactions.
• What would be the formal charge/oxidation number for the oxygen in these exercises. I paused the video and tried to work it out. Here is my reasoning:

Formal charge - Oxygen has six valence electrons and two bonds. So the formal charge would be 6 - 2 = 4

Oxidation state - Oxygen has six valence electrons and two bonds. It is the more electronegatative element for both bonds. Therefore, it's oxidation state would be 6 - 2 - 2 = 2

Is this correct?
• No. They are not drawn, but each oxygen has two sets of lone pair electrons.
Formal charge = 6 VE - 2(from two bonds) - 4 (from lone pairs) = 0
Oxidation state = 6 VE - 4 (from two bonds with less electronegative atoms) - 4 (lone pairs) = -2
• does the free end of the structure always represent methyl group?
• If the structure ends in a line and no other element is specified, it's a methyl group
• What is the use of formal charge and oxidation charge? I understand how to do it, but I don't know why we need to do it.
• formal charge help us to understand how much cordination covalent bond we have in compond
• why do we need concepts like oxidation states, and formal charge.?
• They help us keep track of electrons during reactions and often help us to predict the atoms at which reactions will occur.
• Since alcohols have a OH bonded to it are they basic?
• they are lewis bases but not because of the OH but because oxygen has lone pairs he can donate to lewis acids. they are also acidic because they can donate a proton making strong alkoxyde base in the process.
• At he says "methanol." I know this is a pretty elementary question, but why does methanol end in "ol"? As for a question actually pertaining to the video, does anyone have classic examples of molecules being used to teach oxidation states. (like practice problems?)
• Methanol is a combination of the base "methane" plus an alcohol group, which tends to be simplified in nomenclature by "ol". Thus, we have methanol.
• can we see carbon structures by any equipment or are they imaginary structures?
• The equipment exists that allows us to see fuzzy images of molecules.
However, for the most part, we imagine that molecules have the shape they do because all their chemical and physical properties are consistent with those structures.
• Would the carbon atom be quote unquote "satisfied" with a certain number of electrons and as a result not attract all 6 electrons to it? Is that the definition of polarity?
(1 vote)
• Well the carbon is satisfied with the number of electrons it has in methanol. It has an octet (8) of electrons from bonding with the hydrogen and oxygen atoms. It’s sharing those eight electrons with the hydrogen and oxygen atoms in covalent bonds, but the sharing isn’t equitable. Certain elements have more attraction to electrons than others and so the electrons end up spending more time around one atom compared to the other in a bond. Electronegativity is the measure of this attraction elements have for electrons. In a covalent bond, the bonding electrons spend more time around the more electronegative atom as opposed to the less electronegative one.

Being polar in this context means one end has an excess of negative charge while the other has a lack of negative charge (or is positive). Individual bonds can be polar if the bonding atoms have a high enough electronegativity difference, and therefore the more electronegative atom pulls much stronger on the electrons than the other. Entire molecules are most often where we use polarity and it describes a molecule with a negative and positive pole (or side). For a molecule to be polar it requires polar bonds and certain molecular geometries so the dipole moments of the polar bonds don’t cancel.

Formal charge and oxidation number are just convenient ways of assigning electrons to atoms in molecules. The only difference between the two is that formal charge doesn’t take into account electronegativity, while oxidation number does. Both of these system simply account for electrons to make the math simpler. Regardless of what system we use, the carbon is still satisfied because it has an octet of electrons.

Hope that helps.